Engine Performance problem
1994 Chevy Suburban V8 Two Wheel Drive Automatic 200000 miles
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I have a 94 Suburban that has had the engine replaced about 2 years ago. All was running fine until last week. I took the vehicle in to get the oil changed and it has not performed well since. The station that did the oil change also cleaned the throttle body. It has oil recommended for high mileage engines. When going up hills, it will down-shift, RPMs will go up, but it will not accelerate up the hills. Any recommendations will be appreciated.

Thank you.